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Some HVAC thoughts from me for a change vs. building envelope chatter:

Reading your postings above, you want high quality filtration along with modulation ability for your HVAC. Seems chilled water might be a good selection for that, as you can set up one or two air handlers with high MERV or HEPA filters, and as long as all of your ducts are within conditioned space, run the blower continuously to get constant filtration of the air. Modulate chilled water flow so your coil is always cool to cold during cooling season, so it can control space temp and dehumidifiy. You won't have the potential freeze-up problems using chilled water vs. DX, and you won't have a wet coil dumping moisture into the space when the compressor cycles off, since you would still flow chilled water through the coil during the compressor off-cycle. The amount of chilled water itself can be modulated to control zone temp, as long as the coil stays cold enough to dehumidify. Fresh air can be ducted into the return side of your AHUs.

A redundant question, perhaps, but would a supplementary dehumidifier be required with a chilled water system in a place like Houston or could a chilled water system provide all of the dehumidification for a 'modern' home?

Obviously, there are a ton of application- and building-specific variables at play here, but is it "common" in a hot-humid climate for residential applications?

A redundant question, perhaps, but would a supplementary dehumidifier be required with a chilled water system in a place like Houston or could a chilled water system provide all of the dehumidification for a 'modern' home?

Obviously, there are a ton of application- and building-specific variables at play here, but is it "common" in a hot-humid climate for residential applications?

No, you would not need a separate dehumidifier with a properly controlled chilled water system. The key is having reheat after the cooling (which is the only thing that makes a dehumidifier different than an air conditioner). With dehumidifiers, it used condenser heat for the reheat. With chilled water, it can use hot water, of chilled water return. As mentioned earlier, chilled water is NOT common YET in residential construction (not by the volume numbers). But it is used often enough in larger or higher dollar that require many zones, and the components are available. Recirculating water (hydronic) systems are very common in homes, so most the components are made in very high volumes. The difference is most of those hydronic systems are used for heating instead of cooling. Most the components are universal between heating and cooling (pumps, tanks, valves, etc). The only difference is the temperature of the water flowing through them. The manufacturers that make the chillers (multiaqua, unico, etc) also make the other 'specialty' components required - the 4-pipe (for cooling and reheat) fan coils, and/or air handlers. Controls on a system like this is going to be a 'custom' - albeit relatively simple - design - but it's the controls that directly give you the comfort gains.

I oversee equipment for an art museum where humidity control is crucial to protect the collection. We do almost all of it with chilled water. The only place we don't is in a cold vault kept at 20 degrees, where we use a desiccant wheel instead. So yes, you can control a building's temperature and humidity nicely with chilled water. It's all in how you set everything up to do it.

Fresh air should go through the AHU or a dehumidifier first to condition it before it hits the space. A slight positive pressure helps keep infiltration rates down. Infiltration is outside air that does not go through the unit first and is a source of heat gain/loss, drafts, and humidity. It's better to remove the humidity before it can work into furniture, paper, clothes, etc in a room.

Zoning with air is an option with chilled water but you may get better diversity for outdoor unit size reduction out of FC units. Also, another thing to consider is that piping is a more efficient form of energy transfer than ductwork by far (look at the size of a pipe verses a duct to carry the same btuh).

Look at circulators like the Grundfos Alpha that can adapt flow as the units are satisfied and valves close. This eliminates the need for or can reduce the size of a bypass valve on a small chilled water system and saves energy by reducing rpms automatically as flow is reduced. Reduces or eliminates the need for balancing the system other than a basic setup.

are cost differences between water cooled and mini split close
or would cost be closer to regular hvac system?

I'm reading & learning too. the only water cooled centrals I've
seen in resi is freus units. more in commercial and of course larger
setups.

just trying to get an idea of cost comparisms without violating rules.
great postings crazifuzzy & all.

You might notice that I keep mentioning equipment diversity as a potential for cost savings with the mini chiller setup. I had a high mass building with 18" thick uninsulated walls that I designed a mini chiller system for. I performed a Life Cycle Cost Analysis of the mini chiller, VRF, and thru window AC units, (ducting was not an option due to lack of ceiling space, so a central station AHU was not an option).

The existing system was 12 (1/2, 3/4, 1 ton) window units over 3 floors totaling about 9 tons connected load approximately 5 tons actual with diversity and varying peak times, infrastructure for window units was all in place (electrical connections, window supports etc). So window units won hands down as the lowest equipment cost first cost option. VRF allowed us to use a 7.5 ton outdoor unit (diversity allowes for up to 130% connected load on a VRF system), the chilled water calculations showed that as long as the system was allowed to operate fairly continuously 24/7 and included a buffer tank, we could add 2 rooms for a total of 6.5 tons actual load and 11 tons connected load and reduce the outdoor unit to a 5 ton heat pump chiller, becoming the lowest life cycle cost option and the system that was installed. With the thick walls contributing flywheel effect and a small buffer tank, the system operates just fine.

If I remember correctly, the equipment costs are similar for equally sized VRF and mini chiller, but the mini chiller sales guy claimed lower installation costs, especially if PEX piping is used.

He also claimed lower maintenance costs because VRF systems are largely proprietary and much of the service and parts have to come from the equipment vendor using factory certified technicians. These mini chillers are not as complicated. They just make cold water, not precisely meter out refrigerant as needed.

If I remember correctly, the equipment costs are similar for equally sized VRF and mini chiller, but the mini chiller sales guy claimed lower installation costs, especially if PEX piping is used.

He also claimed lower maintenance costs because VRF systems are largely proprietary and much of the service and parts have to come from the equipment vendor using factory certified technicians. These mini chillers are not as complicated. They just make cold water, not precisely meter out refrigerant as needed.

How big of a buffering tank did (do?) you use and are there any specific kinds of insulated tank that are better for this? Quick math seems to indicate that a 50gal tank provides about 10K BTU of reserves with a 72*F setpoint. Of course, there will be standby losses, and I'd expect to want/need a decent reserve for the hottest days. A very interesting idea!

Heck, I would just appreciate an invitation to the party when the installation begins, this will be one of those "seeing is believing" installs no doubt "if" it all works out. Of course the a/c system cost may tower over the complete home build cost by the time it's all said and done, but what the heck, it's only money and you can't put a price on comfort, right?

__________________________________________________ _______________________“Experience is a hard teacher because she gives the test first, the lesson afterwards". -Vernon Law-

Heck, I would just appreciate an invitation to the party when the installation begins, this will be one of those "seeing is believing" installs no doubt "if" it all works out. Of course the a/c system cost may tower over the complete home build cost by the time it's all said and done, but what the heck, it's only money and you can't put a price on comfort, right?

So what part of the system is going to add this exorbitant cost? This is not some experiment in new technology, it's applying tried and true technology to a different sized envelope. Thermodynamics work regardless of the size.